Capital and income breeding

[4] A different example of the interaction between capital and income breeding is found in Vipera aspis; although these snakes are capital breeders, they lay larger litters when food is abundant, which is a characteristic of income breeders.

[5] The dichotomy between income and capital breeders was introduced in 1980 by R. H. Drent and S. Daan[6] to explain why birds usually laid their eggs later than the time that would maximize nestling survival for the population.

Similarly, the possibility of decreased agility or increased conspicuity associated with, for example, egg-carrying could increase predation on reproducing individuals, making a strategy based on capital breeding more favourable, so as to avoid having to forage while reproducing.

[10] Endotherms have a higher level of energy that needs to be dedicated to maintenance, thus explaining their increased reliance on income breeding.

Both systems fit with the optimal time of laying for low-quality and high-quality individuals.

The length of the feeding season also selects for size in these organisms; income breeders are as small as possible so they can take advantage of having multiple generations per breeding season, in contrast with capital breeders, which are as large as possible so as to catch the most food to put into their reserves.

Timing of breeding in birds relying on capital breeding. The dashed line shows an example of an individual increasing in condition, while the solid line shows the threshold of when the individual breeds.
Timing of breeding in birds relying on income breeding. The dashed lines shows two examples of individuals increasing in condition (one faster than the other), while the solid line shows the threshold of when the individual breeds.